Studies on the relationship of structure and function of the Ca2+ pumping ATPase of erythrocyte plasma membranes will be continued. This Ca2+ pump is the archetype for plasma membrane Ca2+ pumps from heart, other muscle, kidney, brain, intestinal epithelium and several other cell types; all of these cell types contain plasma membrane Ca2+ pumping ATPases closely resembling that from the erythrocyte. This enzyme consists of a single polypeptide chain, Mr = 140,000; it is possible to obtain it pure and in reasonable quantity from human erythrocytes. We propose studies designed to create a map of the primary structure of the enzyme, and to locate the various functions of this enzyme on the map. Studies will also be carried out on the regulation of the enzyme by the lipids of the phosphatidylinositol cycle and by proteolysis.